The overall objective of this research is to determine how the expression of the genetic information contained in animal viruses is regulated within mammalian cells. I am interested in elucidatng the mechanisms by which viral RNA genomes are replicated and transcribed as well as how these two processes are regulated. I propose to investigate the process of viral RNA replication with the use of defective interfering (DI) particles of VSV. Most DI particles have the advantage that, in the presence of the helper virus, they only replicate but are not transcribed. Hence, one has the opportunity to study RNA replication independently from transcription. The experimental approach will be to isolate and characterize the RNA and protein components of the replicative intermediates that form within the infected cell. We will attempt to use these isolated complexes to develop an in vitro replication system to study both replication and interference of DI particles. To study how host component(s) are involved in VSV RNA replication, I plan to examine VSV replicating structures for the presence of host factors and to investigate the mechanism by which poxvirus reverses the block of VSV replication that occurs during the infection of rabbit cornea cells.